1. Field of the Invention
The present invention relates to a solid-state image sensing device, a method for reading out a signal of a solid-state image sensing device, and an image pickup apparatus and, in particular, to a solid-state image sensing device for reading out a signal output from each of the columns of an array of unit pixels while amplifying the signal using a signal readout circuit unit, a method for reading out a signal for use in the solid-state image sensing device, and an image pickup apparatus using the solid-state image sensing device.
2. Description of the Related Art
It is difficult to reduce the area of a circuit portion of solid-state image sensing device, such as complementary metal oxide semiconductor (CMOS) image sensors, and reduce noise occurring in the circuit portion at the same time. Existing CMOS image sensors include a signal readout circuit unit (a column processing unit) provided for each column of a pixel array of a pixel array unit. In a related art, in order to reduce noise of CMOS image sensors, the signal readout circuit unit amplifies a signal having a narrow noise bandwidth by performing computation using a switched capacitor circuit and a capacitance ratio. Thereafter, the signal readout circuit unit reduces the noise by computing the equivalent input power of the amplified signal (refer to, for example, Japanese Unexamined Patent Application Publication No. 2005-269471).
As shown in FIG. 20, in existing CMOS image sensors, the signal readout circuit unit includes unit readout circuits (signal readout circuit units) 100 (100-1 to 100-n), each including an operational amplifier 101, control switches 102, 103, and 104, an input side capacitor 105, and a feedback capacitor 106. One of the signal readout circuit units 100 is provided to a corresponding one of n columns of the pixel array of a pixel array unit. Signals Vin[1] to Vin[n] output from the columns (the unit pixels in the columns) are amplified by the unit readout circuits 100-1 to 100-n and are read out.